1. Field of the Invention
The present invention relates to an image reading apparatus in which a pressing plate can be discharged, and also to a multi-functional apparatus having such an image reading apparatus.
2. Description of the Related Art
Recently, a multi-functional apparatus having an image reading apparatus, an image forming apparatus, a facsimile apparatus, and the like is widely used. In such a multi-functional apparatus, in order to further reduce the cost, the number of parts is reduced, or more economical parts are used. While realizing a low production cost, it is intended to enhance the performance to be equal to or higher than that of the conventional art.
In an image reading apparatus mounted on a multi-functional apparatus, for example, an expensive CCD image sensor is not used in an operation of reading an original serving as a medium to be read, and the reading operation is conducted with using a contact image sensor (hereinafter, abbreviated to “CIS”) which is more economical. A CIS has a shallower depth of field than a CCD image sensor. In order to read an image without blurring, therefore, an original must be in close contact with a CIS. In an image reading apparatus, consequently, a pressing plate for urging an original against a CIS placed in a transport path through which the original is transported is disposed, and the original passing over the CIS is pressed against the CIS by the pressing plate, whereby close contact between the CIS and the original is realized.
Such a pressing plate is formed of a sheet metal or the like in order to ensure the strength of enabling the movement. In the pressing plate, a white sheet made of polycarbonate, vinyl chloride, or the like is bonded to a portion which is opposed to the CIS. The white sheet is used as a reference of the reading brightness for the CIS. During the process of reading an original, the white sheet always butts against the original, and therefore is easily charged by friction with the original. In JP-A-2001-217988, a movable pressing plate (original pressing means) is always set to a contacting state by a white ground compression spring, and the white ground compression spring is connected to a ground line through plate springs and the like to be grounded, thereby discharging the pressing plate.